A transfer press, i.e. a press machine installed with a plurality of processing stations within its press body, is provided with a workpiece transfer device that transfers workpieces in sequence among the processing stations. The workpiece transfer device includes a pair of transfer bars mounted in parallel with a direction in which workpieces are transferred, each of the transfer bars being provided with detachable workpiece holders capable of holding and releasing workpieces depending on a position and a type of dies disposed in respective processing stations.
The dies need to be replaced according to a type of the workpiece (type of product). A lower die, the die normally installed on a moving bolster, is transferred from the press body to the exterior together with the moving bolster, simultaneously with an upper die that is released from a slide. In other words, when replacing the dies, dies are changed to desired ones by a die-replacing work, or the moving bolster is replaced with another one already installed with predetermined dies.
In the meantime, the workpiece holder that has to be replaced depending on a type of workpiece as in the case of the dies needed to be replaced with in the press machine because the workpiece holder is mounted on the transfer bar of the workpiece transfer device that is independent of the moving bolster. While replacing the workpiece holder, the press machine was unable to operate, causing a roadblock to an improvement in operating rates of the press machine. Hence, the transfer bar is separated into a movable bar positioned in the middle and two fixed bars at both ends, allowing the workpiece holder to be transferred to the exterior and moved back inside along with dies by the moving bolster together with the movable bar on which the workpiece holder is mounted.
Many of connecting mechanisms in which a detachable movable bar and fixed bars (hereinafter referred to as remaining bars) are connected are ones in which a plate-shaped engagement member provided on the remaining bars is locked with an engagement body of the movable bar as disclosed in the below Patent Literature 1. For other information, Patent Literature 2 discloses a mechanism, in which plate-shaped connectors of the remaining bars and another connector of the movable bar are connected by a pin disposed in a vertical direction perpendicular to a longitudinal direction of each of the bars, while with respect to a vertical direction of the two plate-shaped connectors, dampers on the remaining bars function as holding means, enabling three-dimensional binding of the connectors in each direction.